1. Field of the Invention
The present invention relates to an electro-mechanical transducing element, and more particularly to an electro-mechanical transducing element which is mechanically deformable in response to an electrical signal, and to a mechanically moving portion in which the element is used.
2. Description of the Prior Art
Using the piezoelectric effect of a piezoelectric ceramic plate is well known.
A piezoelectric ceramic plate is formed of a polycrystalline material having a high dielectric coefficient. The piezoelectric property of the plate is polarized in a predetermined direction and exhibits a unique mechanical property when a voltage is applied to the plate. For example, when a voltage is applied to a thin and long piezoelectric ceramic plate provided on a substrate of metal or the like in the same direction as that of the polarization, the piezoelectric ceramic plate shrinks in the lengthwise direction, while the substrate does not change. Accordingly, piezoelectric ceramic plate deflects together with the substrate and the shift is produced by the mechanical deformation. To increase deflection, two piezoelectric ceramic plates can be combined. A voltage is applied to one plate in the direction of polarization and to the other plate in the reverse direction to that of polarization. A electro-mechanical transducing element including a pair of piezoelectric ceramic plates combined as mentioned above is known as a bimorph element. Such a bimorph element has a greater deflection than the electro-mechanical transducing element with a single piezoelectrical ceramic plate. A so-called push-pull effect is realized. Furthermore, it is possible to reverse the direction of deflection by reversing the polarity of the applied voltage.
U.S. Pat. No. 4,151,569 to Hathaway discloses an example of the application of such an electro-mechanical transducing element and, more particularly, a bimorph element to an apparatus requiring a large degree of deflection in both directions, such as a video tape recorder, a video disc recorder or the like. To effect proper reproduction of information recorded on a recording track of a tape or disc, it is necessary to position a reproducing head correctly on the track to be read out. It is then possible to use a bimorph element to adjust the head position for aligning the head with the recording track to be read out on the recording medium.
In a head moving device using a bimorph element such as disclosed in U.S. Pat. No. 4,151,569, the bimorph element is supported at one end, while its free end is fixed directly or via a printed circuit plate to the head. Signal wires are then connected to a coil of the head either directly or via the printed circuit plate. However, the fact that the lead wires are connected near the free end of the bimorph element, where the maximum shift is obtainable, causes an increase of the load on the bimorph element, because the lead wires themselves have a certain rigidity. Accordingly, this has a bad influence on positional control for the head by the bimorph element. For example, a desired shift of the head cannot be obtained or a larger drive voltage is necessary to obtain the desired shift of the head. In addition, the fact that the lead wires are connected near the free end, where the maximum shift of the bimorph element is obtainable, results in inferior connection, breakage, or the like, of the lead wires through usage over the years. Furthermore, the fear exists that when the head is vibrated, the resonance frequency of the bimorph element would lower due to the damping effect of the lead wires and the available frequency range would narrow.
It goes without saying that such inconvenience arises not only where the object to be moved is a magnetic head but also generally where an electrical lead wire is connected to an electrical member provided near the free end of an electrical-mechanical transducing element support at another end.